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Month: October 2012

I have a new toy that came in two weeks ago: it’s a Full Spectrum 40W hobby laser cutter! It has been sitting in the shipping box for all this time. This weekend I finally gather everything I needed to set it up, and here are some fresh-made engravings:

Not too bad for the first try, isn’t it?

Impression. My order was handled very quickly. I placed the order on a Tuesday after 5pm and it was shipped the same day! A big thumb-up to the Full Spectrum team. A week later, the box showed up at my door. It’s quite big and heavy. I mean, this is already the least expensive, hobby level model on the market. I can easily imagine how daunting the professional level ones must be.

Setup. The build quality is pretty good. The exterior could probably use some more sexy design, but at its price level, I have no complaint. To set it up, I bought a stainless steel table from Ikea, a 5-gallon bucket with cover from Lowes, and five gallons of distilled water. The user manual stressed everywhere that you must use distilled water and not tap water. It is used to cool down the laser tube. I guess distilled water is crucial to avoid sediments.

The user manual is a bit confusing and not entirely consistent. Some pictures do not match my model I ended up having to check some youtube videos and forum posts to figure things out. Also, the instructions for installing the beam combiner are almost unreadable due to low toner. This is a bit disappointing. The good news is that these instructions are all available online, so it’s not a big deal.

There are three peripheral devices I set up first: air compressor, water pump, and exhaust fan. Air compressor is the easiest: just connect the air tube and that’s all. For setting up water pump, I cut three holes on the cover of the bucket, so that the in/out tubes and the power cable can go through the cover easily. Then I placed the water pump in the bucket, and poured 5 gallons of distilled water. The exhaust fan is also fairly easy to set up. The only tricky part is to find a way to vent exhaust air to the outside. My solution is to use a piece of cardboard paper and cut it to the right size so that it can fit tightly on my window. Pictures are included:

Running. The first thing to do is to manually move the Z-table in order to get the laser focused onto the engraving surface. I followed the instructions to do a fire test and it worked right away. Keep in mind that the water pump, air compressor, and exhaust fan MUST be running before the laser fires. Also make sure that the emergency stop is deactivated, and the laser switch is activated. The control is done through USB port, which is very convenient. (I remember my hobby CNC machine requires a hardware parallel port, which was a pain to find). The software is only available on Windows. Since I am mainly using Linux these days, I had to salvage an old Windows PC for this. I suspect I can probably run it through a Virtual Windows on my Linux machine too. The software is reasonably good. It did give me annoyance like hanging and crashing, but nothing that can’t be fixed by restarting the laser cutter and software. Here is a video demo of the machine in action:

As you can see, my first test case is to engrave the OpenSprinkler logo (courtesy of Nathan Johnson) onto the project enclosure. It took me a few tries to find the right laser power level and speed. No rocket science. The enclosure material is probably not best designed for laser engraving, because it can easily burn and produce a greenish color. But at the appropriate laser intensity, it looks reasonably good.

The next order I ship will include this engraved project enclosure 🙂 I can probably start making a small batch of engraved enclosures if it turns out to be reasonably productive.

My next steps are to try laser cutting, and installing the beam combiner. Overall I am pretty happy with this new toy. Given that this is the first time I’ve ever used a laser cutter, I would say the installation and initial tests went very smooth. Again, a thumb-up to the Full Spectrum team.

Recently I received a request to customize OpenSprinkler for a 12V DC external relay board. It turns out to be relatively easy to do. Since it may be useful for other folks, I am writing a post here to briefly describe the modifications. First of all, the relay board has built-in opto-couplers and flyback diodes. It is designed to work directly with microcontroller pins. This particular relay board I received is an active low type. This means normally the relay control pin is pulled high; when the control pin is set low by the microcontroller, the relay will be activated. So before you go ahead and make changes, make sure to find out the type of your relay board.

OpenSprinkler can run on 12V DC power supply without any modification. As long as you keep in mind the polarity, it should work right away. Even if you connect the power supply in the wrong direction, it shouldn’t cause any damage because there is a protecting diode D1 that prevents reverse polarity. The only modification I needed to do is to replace the triacs (used to drive AC solenoids) by NPN transistors. Any common NPN transistor is fine. For example, 2N3904. The remaining step is to connect the station wires to the corresponding relay control pins.

The way it works is that normally the shift register outputs low. So all NPN transistors are turned off, and the collectors are pulled high by the relay board. When a station is open, the shift register pin outputs high, turning on the corresponding NPN transistor, and driving its collector low (to ground). This in turn activates the relay. That’s it.

Here is a video showing the relay board in action. The OpenSprinkler running a self test that turns on each station for 3 seconds.

It is also possible to use the NPN transistors to directly drive the relays. However, in this case, you need to add an additional flyback diode (between the collector of the transistor and the +12V line). The flyback diode is important to protect the transistor under inductive load. To accommodate this, I am planning to add PCB holes for these diodes in the future, which will make it easy to solder these extra components.

Hi, I am excited to announce the arrival of SquareWear — a new open-source microcontroller board I designed for wearable electronics projects. First off, here is an introduction video:

Background. So why did I work on this? Well, last year I helped my school with several wearable electronics workshops. They were great success: the students had a lot of fun sewing LEDs and sensors onto clothes, and many women students came to attend the events. We used Lilypad Arduino, which is a popular microcontroller board designed for wearable computing projects. It’s a very nice design, but using it for a 40-student workshop presented a few challenges. First is the cost. Lilypad itself costs about $20, which is ok. But to program it, you need to get an external FTDI cable, which costs another $15. We want students to take the gadgets with them after each workshop. But since we had a small budget, we couldn’t afford to buy one set for each student. So we had to let every 2 students share a set. Not everyone was happy about it. Second is FTDI driver issues. You would think this is easy, but it turned out that at the beginning of each workshop, we had to spend 30-40 minutes just to help everyone install FTDI drivers. Students were using all sorts of operating systems and having all sorts of unexpected problems. Some were even using pre-beta version of Windows 8 64-bit… Anyways, it was not fun. What I really wanted is a board that does not need any driver installation. Whether you are using Windows, Linux, or Mac, the system should recognize the device automatically. Next is the number of external components required. Many students started designing beautiful LED patterns that involve a lot of parallel LEDs, only to find out later that the LEDs looked really dim. Why? The standard microcontroller pin can only source or sink 25mA of current. If you have a string of 20 LEDs, they will not look bright because of the current limit. The better solution is to use a transistor or mosfet to allow switching higher amount of current. Because switching LEDs is very common task in wearable electronic projects, it would be nice to have mosfets as built-in components on the board. Similarly, some students wanted to include push-buttons to their projects, but the push-button on Lilypad is only for reset, not for general-purpose function. Lastly, it would also be nice to have an on-board coin battery option, because coin batteries are cheap and easy to find in local stores.

So these experiences motivated me to develop my own wearable electronics board, and here comes the SquareWear!

Features. The name SquareWear comes from its shape: a 1.6″x1.6″ square. Credits should be given to my colleague Andrew who came up with the name. Officially it’s Square-Wear, but it could also be Square-Ware, either way you like. I made it with a few different colors and two battery options: a coin battery version, which runs on a built-in CR2032 battery, and a li-po version, which runs on an external li-po battery. Each board has a built-in USB port, which is used for multiple functions: programming the microcontroller, USB serial communication, recharging battery (li-po version), and providing power directly. No external FTDI cable any more! The microcontroller is pre-flashed with Microchip’s USB HID class bootloader, which requires no driver installation, whether you are using Windows, Linux, or Mac. In addition, SquareWear has four power sink pins wired to on-board BS170 mosfets. These four pins support up to 500mA load, which makes them suitable for driving many parallel connected LEDs. Using these power sink pins, your LEDs will look nice and bright. Lastly, there is an on-board push-button that you can use as a general-purpose button. In sum, I designed all these features to make SquareWear a low-cost, all-in-one solution for wearable electronics projects. You can get started right away without having to worry about external components or programmers.

Programming. SquareWear runs Microchip PIC18F14K50 microcontroller. What? It’s not based on Arduino? Why? Well, let me explain. The project started as I was shopping around for different microcontrollers. My friend Christian recommended me to look at PIC. Around the same time I also started designing my own wearable electronics board. At one point I realized I should build the wearable microcontroller board using PIC, because this will be a good motivation for me to learn PIC programming. I chose 18F14K50 to begin with, because it’s among the lowest-cost microcontrollers that have built-in USB support. As I got more familiar with it, I started liking it more and more. It has a decent amount (16KB) of program memory space, not a whole lot, but sufficient for most entry-level wearable electronics projects. It has a decent number (12) of i/o pins, again, not a whole lot, but enough to fit all pins on a small PCB without wasting any. Most importantly, it has Microchip’s USB bootloader and serial communication support. So this naturally became my choice for SquareWear.

Another reasons I went with PIC is that its programming environment – MPLAB X – is a fully-featured cross-platform IDE. It has all the features of a standard IDE, such as code navigation, context aware code completion, debugging, and support for project files and library files. I like using standard IDEs. I think Arduino is great for beginners, but there is no code navigation and completion, and debugging is only possible in printf style. If you are serious about learning to program, you should start using professional tools. I would like to use SquareWear as a way to introduce programming to students, and I think it’s important to get them exposed to standard tools right in the beginning. It will require a slightly higher learning curve, but it’s absolutely worthwhile.

SquareWear Library. I spent quite some time writing the SquareWear Software Library, making it simple to use just like the Arduino. It abstracts away a lot of low-level programming details. I also included several features, such as software PWM, timer interrupt, button interrupt, software reset, which I feel are very useful for wearable projects. Take a look at the SquareWear Demos and the Programming Reference to find out more.

One downside with using 8-bit PIC is that its compiler C18 is a C compiler, that is, not C++. So there is no object-oriented programming, which may appear disappointing. But it’s not a show stopper: we all like the benefits of object-oriented programming, but there are tons of microcontroller projects that are written in plain C style perfectly fine. Particularly with respect to wearable projects, they are typically quite simple. There is no need to use objects, inheritance, function overriding, and all those good stuff. So no need to panic because of the lack of C++.

The last thing to mention is that just like my other projects, SquareWear is completely open-source: the hardware design and software code are all available on GitHub. Beyond wearable electronics projects, SquareWear is also a great little tool for general prototyping need, like interfacing with sensors and actuators. Give it a try and hope you like it!

OpenSprinkler’s 1-year anniversary! Yes, on Oct 9 last year, the OpenSprinkler project got posted on Hackaday and became known to the world for the first time. A lot of updates have happened during this past year. The hardware has gone through four cycles of changes, and the latest version is 1.4. From August 2011 we have started producing the surface mount version of 1.4, making it easier to manufacture and assemble the kit. The software has also been substantially improved. Many user-requested features have been included. I am proud to say that at this moment OpenSprinkler is probably the best Internet-based sprinkler timer with its price and the functionality it provides. I am hoping that in the upcoming years it will start making a positive impact on the technology innovation in consumer-level sprinkler products.

To honor the 1-year anniversary, all orders placed on Oct 9 (today) and 10 will receive a 10% discount. If you have ever considered buying OpenSprinkler but hasn’t made up your mind, there is no better deal than this!

Statistics wise, most OpenSprinkler orders came from the United States, which is not a surprise since we are based in the US. But OpenSprinkler has also reached places outside of the US. So far it has reached close to 30 countries. Here is an un-ordered list: Germany, Netherlands, Australia, South Africa, France, Bulgaria, Spain, Slovakia, Canada, UK, Finland, Portugal, Hungary, Singapore, Belgium, New Zealand, Italy, Turkey, Greece, Peru, Switzerland, Cyprus, Ukraine, Denmark, Estonia, Poland, Austria. I have also marked them on a world map, to give you a better visual:

I want to take a moment to thank the open-source movement. I am a strong supporter for open-source hardware and software. I believe open-source is important for pushing technology innovation and for promoting and implementing new ideas as quickly as possible. Unlike large-scale closed source products, open-source products are often started with a low budget and produced in small batches. We typically assemble kits on the level of a couple hundred per batch. This is how we can quickly update the design, fix bugs, introduce new features, and shorten the overall design cycle. If a particular design didn’t work out, we can simply abandon it and move on. There is little risk of losing big investment money. Also, having a project open-sourced makes it possible for the public to scrutinize the design, identify issues, contribute to the project, and build new projects. As a college educator, I am keen at understanding the underpinnings of how electronic products work, but more than that, I am keen at giving out the knowledge that I know.

Update: OpenSprinkler 2.0 or above uses a different switching regulator and does not require additional resistor any more. The information below is only relevant to OpenSprinkler 1.x.

As you know, OpenSprinkler uses a single 24VAc sprinkler transformer to power both the circuit and the sprinkler solenoids. Frequently people are using a WiFi adapter together with OpenSprinkler to provide wireless Ethernet connection. So how about using the same transformer to also power the WiFi adapter? Ah ha, good question. This turns out to be possible and quite easy to do!

The basic idea is that many of these WiFi adapters (such as the popular NetGear WNCE2001) can be powered using an attached USB cable. One end of the cable is a USB Male A connector, and the other end is typically a 2.5mm power jack that goes into the adapter. Since OpenSprinkler has a built-in USB port (which is connected to the +5V output of the 34063 switching regulator), it can be used to directly power the WiFi adapter. However, OpenSprinkler’s USB connector is a Female B type, so the trick to make this work is to throw in a USB Female A to Male B converter, as shown in the picture below:

You can get this converter from Rayshobby Shop or at online retail stores.

Hold on one second, this is not the only thing you need to do. You also have to solder an additional 1 ohm resistor to the circuit board. The reason is that these WiFi adapters are quite power hungry: I measured that the NetGear WNCE2001 draws about 300-400mA current during operation. On the other hand, OpenSprinkler (by default design) outputs about 330mA current on its +5V output, of which 180mA will have to power the mcu and Ethernet controller. So we need to increase the current output. Fortunately this is not too difficult to do. The trick is to reduce the resistance of Rsc — current limiting resistor for the 34063 switching regulator. According to 34063’s datasheet, the maximum output current is 0.33/Rsc. So if we put two 1 ohm resistors in parallel, Rsc is effectively 0.5 ohm, and hence the maximum output current increases to 660mA, enough to power both the circuit board and the WiFi adapter. Also, OpenSprinkler v1.3u and v1.4 have already designed a spare slot for the parallel Rsc, so it’s pretty easy to make the modification.

You can reduce Rsc even further to provide better safety margin. 34063 supports maximum output current of 1.5A. To do so, you can keep putting more 1 ohm resistors in parallel until you reach the desired resistance. The reason to use multiple 1 ohm resistors is because it’s lowest value common resistor. Anything below 1 ohm will have a big price jump.

Again, if you are interested in trying this, you can get the USB converter from Rayshobby Shop. We will also throw in a couple of 1 ohm resistor free of charge!